def Constructor():
    symboldict={
            'SP'  : 0,
            'LCL' : 1,
            'ARG' : 2,
            'THIS': 3,
            'THAT': 4, 
            'R0'  : 0,
            'R1'  : 1,
            'R2'  : 2,
            'R3'  : 3,
            'R4'  : 4,
            'R5'  : 5,
            'R6'  : 6,
            'R7'  : 7,
            'R8'  : 8,
            'R9'  : 9,
            'R10' : 10,
            'R11' : 11,
            'R12' : 12,
            'R13' : 13,
            'R14' : 14,  
            'R15' : 15,
            'SCREEN' : 16384,
            'KBD'    : 24576,
            }  
        return symboldict 

def addEntry(symbol, address, symboldict):
    symboldict[symbol] = address
    return symboldict

def contains(symbol, symboldict):
    return symboldict.has_key(symbol)

def GetAddress(symbol, symboldict):
    return symboldict[symbol]
